Correcting lens

ABSTRACT

A correcting lens for use in the formation of a color television picture tube screen that is excitable by an electron beam comprises a plurality of individually contoured elements that extend from a point common to all elements to an edge of the lens. Adjacent elements are separated by boundaries and all boundaries extend radially outward from the common point. Each element is individually contoured to direct light onto predetermined paths of the electron beam toward a similarly shaped corresponding area of the screen.

OR Brant 3 United States P 3,811,754 Morrell et al. May 21, 1974 [54] CORRECTING LENS FOREIGN PATENTS OR APPLICATIONS Inventory Albe" Maxwell Mom"; Frans 791,312 2/l958 Great Britain 350/194 Hekken, both of Lancaster, Pa.

73 A RCA Cor ration, New York. NY. Primary Examiner-John Corbin l Sslgnee p0 Attorney, Agent, or Firm-Glenn H. Bruestle; Dennis [22] Filed: Oct. 18, 1972 mbeck [2i] Appl. No.: 298,642

[57] ABSTRACT [52] U 8. CL 350/189 95/1 R 350/213 A correcting lens for use in the formation of a color [511 In c1. .1 (5021) 3/04 televisk" Picmre tube Screen that is exciable by [58] Field 0 Search 350/!75 R 189 I93 194 electron beam comprises a plurality of individually 356/21 1 95/1 contoured elements that extend from a point common to all elements to an edge of the lens. Adjacent ele- [56] References Cited ments are separated by boundaries and all boundaries extend radially outward from the common point. Each UNITED STATES PATENTS element is individually contoured to direct light onto 2/1971 Yamazaki el al. X predetermined paths of the electron beam tow rd 3 2,999,126 9/]961 Harries et al. 350/189 X Similarly Shaped Corresponding area of the Screen l,952.237 3/1934 3,495.51 1 2/1970 Javorik 350/189 UX 7 Claims, 7 Drawlng Figures PATENTEmAm 1914 SHEET 2 OF 2 Fig. 7

CORRECTING LENS BACKGROUND OF THE INVENTION This invention relates to optical correcting lenses for use in laying down arrays of color phosphor deposits in cathode-ray tubes.

Many cathode-ray tubes have mosaic screens or targets of different light emitting or absorbing material. For example, certain types of color television picture tubes usually include a screen comprising arrays of red, green, and blue emitting phosphor lines or dots, electron gun means for exciting the screen, and a color selection electrode, e.g., an apertured sheet metal mask or a wire grill, interposed between the gun means and the screen. In one prior art process for forming each color array of phosphor lines or dots on a viewing faceplate within a tube having an apertured mask, the inner surface of the faceplate is coated with a mixture of phosphor particles adapted to emit light of one of the three colors (e.g., blue), and a photosensitive binder. Light is projected from a source through the apertured mask and onto the coating so that the apertured mask functions as a photographic master. The exposed coating is subsequently developed to produce phosphor elements of the first phosphor, e.g., blue emitting lines or dots. The process is repeated for the green-emitting phosphor and red-emitting phosphor utilizing the same apertured mask but repositioning the source of light for each exposure. A more complete description of a prior art process for forming a picture tube screen can be found in US. Pat. No. 2,625,734 issued to Law on Jan. 20, I953.

In exposing the screen through the mask apertures, the light source is sequentially placed in a fixed relationship with each center of deflection of each of the electron beams which later will excite the screen. Unfortunately, these deflection centers are not similarly fixed in position but rather vary in position during operation of the tube. One such variation is a shift toward the screen as the angle of deflection increases. This shift of the deflection center parallel to the tube axis causes a radial misregister of the electron impingement spots on the screen with respect to their corresponding phosphor dots established using a fixed light source.

In the case of a dot screen where three beams are subjected to dynamic convergence, an additional type of deflection center shift occurs. This additional shift is transverse to the tube axis and causes degrouping (e.g., an increase in size of the electron spot trios) misregister of the electron spots related to their associated phosphor dots. These and other types of misregister are discussed in greater detail in the following U.S. Pat. Nos.: 2,885,935 Epstein et al. and 3,282,691 Morrell et al. In order to correct error between the position of electron beam landing and the location of a phosphor dot, the prior art has provided correcting lenses located between the light source and the tube screen which provide appropriate deflection of the light rays so as to locate the position of the phosphor dots at the expected landing positions on the screen of the electron beams.

The design of correcting lenses for use in fabricating color television picture tubes has been described by Epstein et al. in U.S. Pat Nos. 2,817,276 ,and 2,885,935, by Ramberg in US. Pat. No. 3,279,340 and more recently by Yamazaki et al. in U.S. Pat. 3,628,850. The lenses disclosed in the latter two patents have discontinuous surfaces that permit more accurate exposure of the screen. However, because of the discontinuities in the lenses, reflection and light scattering occur at the discontinuous interfaces. Since reflection and scatter may cause misregister and uneven exposure, it is apparent that further development of the prior art correcting lenses is desirable.

SUMMARY OF THE INVENTION The present invention substantially eliminates undesirable reflection and scatter by providing a correcting lens for use in the formation of a color television picture tube screen having a plurality of individually contoured elements that extend from a point common to all elements to an edge of the lens.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a correcting lens embodying the present invention;

FIG. 2 is a cross-sectional view taken on line 22 of FIG. 1.

FIG. 3 is a cross-sectional view taken on line 3--3 of FIG. 1.

FIG. 4 is a plan view of another correcting lens embodying the present invention.

FIG. 5 is a cross-sectional view taken on line 55 of FIG. 4.

FIG. 6 is a plan view of yet another correcting lens embodying the present invention.

FIG. 7 is a cross-sectional view taken on line 7-7 of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates a pie-shaped lens 10 formed from eight wedge-shaped elements or segments l2, l3, l4, 19. The lens 10 is used in an optical lighthouse between a light source and a color picture tube faceplate to provide optical correction of the light path so that the light exposes photosensitizled portions on the faceplate at the predicted landing locations of the electron beams of the assembled tube. The surfaces I2, l3, l4 19' of the elements in the lens 10 are individually contoured to provide the best overall optical correction for exposure of correspondingly shaped areas of the color television picture tube screen. Because of this in dividual contouring, each lens element has a considerably different surface shape than its adjacent elements, as shown in FIGS. 2 and 3. Therefore, the lens comprises a plurality of discontinuous interfaces located between adjacent elements e.g., interface 20 between elements 16 and 17, 22 between 17 and 18, 24 between 18 and 19. Each interface consists of an internal portion, where the adjacent elements are in physical contact, and an external stepped portion comprising a part of the surface of the lens. These interfaces could cause reflection inside the lens and at the surface of the lens if light from the light source were to strike the interfaces at an angle. However, when lens 10 is placed in the lighthouse so that its central axis 26 points to or is aligned with the light source, the edges of the interfaces are parallel with the light rays. Therefore, since the lightrays cannot strike the interfaces at an angle, reflection and scattering cannot occur.

Another pie-shaped lens 30, having twelve wedgeshaped elements 32, 33, 34, 43, is shown in FIG. 4. Unlike the preceding embodiment, this lens 30 is formed with a continuous contoured surface 44 as shown in FIG. 5. However, elements in this lens are formed of various materials having different indexes of refraction. Therefore, although the lens surface is continuous, discontinuities in correction can exist between each element because of the differences in indexes of refraction. Optimization of the lens depends not only on appropriate contouring of the lens surface, but also in proper choice of the materials selected for each element. The discontinuities, e.g., discontinuity 46 between elements 38 and 39, 48 between 39 and 40, 50 between 40 and 41, 52 between 41 and 42, and 54 be tween 42 and 43 in this lens 30 are all internal interfaces since the lens has no surface discontinuities.

A third lens 60 is shown in the plan and crosssectional views of FIGS. 6 and 7. This lens 60 comprises a single homogeneous piece of material having only its surface designed in a pie-shaped configuration. The lens surface 61 is divided into twelve sector-shaped surface elements or areas, e.g., 62, 63, 64, 73. Each surface area has its own contour to provide the best optical correction to similarly shaped corresponding areas of the screw. Because of this individual contouring, surface discontinuities or steps exist between adjacent surface areas, e.g., discontinuity 74 between areas 68 and 69, 76 between 69 and 70, 78 between 70 and 71, 80 between 71 and 72, and 82 between 72 and 73. The plane of each discontinuity passes through and is parallel with the axis of the lens. Therefore, when the lens axis points to or is aligned with a light source, the light rays from the source will pass through the lens parallel to the discontinuities and will not reflect or scatter.

The foregoing embodiments can be constructed of any suitable refractive material, e.g., glass or optical plastic. Preferably, lens 30 of FIGS. 4 and can be formed of glass and lens 60 of FIGS. 6 and 7 can be formed of plastic. Such preference is solely dictated by the present state of the art in plastics development (as to lens 30) and by the present state of the art in grinding and polishing of glass lens (as to lens 60). [n a method for forming lens of plastic, the plastic is pressure molded against a suitable die. Such die can consist of segments, corresponding to the lens elements, of a material such as stainless steel that have been ground to conform to the lens specification.

We claim:

1. A correcting lens for use in the formation of a color television picture tube screen comprising a plurality of wedgeshaped elements, a discontinuity between each adjacent element and each of said discontinuities extending from a common point radially to an edge of said lens, and each of said elements being individually contoured for best overall optical correction to light paths for exposure of correspondingly shaped areas of said screen for a source of said light paths on a line passing through said common point and perpendicular to a surface of said lens.

2. The correcting lens as defined in claim 1, wherein said elements include sector surface portions of said lens.

3. The correcting lens as defined in claim 2, wherein said lens is of a single homogeneous piece of material.

4. The correcting lens as defined in claim 1, wherein said elements are individual wedge-shaped parts, said parts interfitted to form said lens.

5. The correcting lens as defined in claim 4, wherein at least two of said parts are of materials having different indexes of refraction.

6. The correcting lens as defined in claim 1, wherein said discontinuities extend through said lens and consist of an interior interface and an exterior surface step.

7. The correcting lens as defined in claim 1, wherein said discontinuities consist only of surface portions of said lens. 

1. A correcting lens for use in the formation of a color television picture tube screen comprising a plurality of wedgeshaped elements, a discontinuity between each adjacent element and each of said discontinuities extending from a common point radially to an edge of said lens, and each of said elements being individually contoured for best overall optical correction to light paths for exposure of correspondingly shaped areas of said screen for a source of said light paths on a line passing through said common point and perpendicular to a surface of said lens.
 2. The correcting lens as defined in claim 1, wherein said elements include sector surface portions of said lens.
 3. The correcting lens as defined in claim 2, wherein said lens is of a single homogeneous piece of material.
 4. The correcting lens as defined in claim 1, wherein said elements are individual wedge-shaped parts, said parts interfitted to form said lens.
 5. The correcting lens as defined in claim 4, wherein at least two of said parts are of materials having different indexes of refraction.
 6. The correcting lens as defined in claim 1, wherein said discontinuities extend through said lens and consist of an interior interface and an exterior surface step.
 7. The correcting lens as defined in claim 1, wherein said discontinuities consist only of surface portions of said lens. 